Antenna



Nov. 8, 1949 N. E. LINDENBLAD 2,487,567

ANTENNA I Filed Sept. 5, 1946 INVENTOR ATTORNEY scripton which is accompanied which:

Patented Nov. 8, 1949 ANTENNA Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application September 5, 1946, Serial No. 695,007

Claims. l

The present invention relates to antennas and more particularly for arrangements for increasing the band widths of antennas. v

An object of the present invention is to improve the wide band characteristics of short wave antennas.

Another object of the present invention is the provision of means for compensating for variations in antenna characteristics with variations in the frequency of radio frequency energy applied to the antenna.

A further object of the present invention is the provision of an antenna for wide band operation which is simple and rugged in construction.

Still a further object .of the present invention is the provision of simple means for both reactance and resistance compensation of antennas designed to operate over a wide frequency band.

When compensating an antenna for variations in its characteristics with variation in the frequency of energy applied thereto in order that the operating frequency band may be widened, it is observed that both the reactance and the radiation resistance of the antenna vary with frequency. The magnitude of said variations as appearing in the transmission line connected to the antenna depends greatly upon the choice of the feed point to which the transmission line is connected and the means by which the transmission line is coupled to the antenna. Even after choosing the optimum feed point and method of coupling, there still remains a certain amount of variation of resistance and reactance with variation of frequency. Additional matching circuits may be supplied for` a further reduction of the impedance variation.

Both reactance and resistance variations of the antenna basically derive from a change in the distribution of the field about the antenna with the change in frequency. However, the reactance variations and the resistance variations tend to follow different laws of variation with respect to frequency changes. It may be said that reactance variations are more easily compensated for, since invgeneral, they can be reproduced in a line element connected to the transmission line. On the other hand, for simpliiied resistance compensation, the compensation should be applied at the source; that is, in the antenna structure itself. I

The present invention will be more fully understood by reference to the following detailed deby a drawing in the antenna.

Figure 1 shows a simple quarter wave radiator I0 extending above ground plane GP which may be a metallic sheet forming a part of the supporting structure for the antenna. Transmission line TL has an outer sheath II connected at its uppermost end to the ground plane GP while the inner conductor I2 is directly electrically connected to the lower end of quarter wave radiator I Here the virtual resistance introduced by radiation at the feed point; that is, in the plane of ground plane GP, is in series with the reactive components of the antenna. Thus, the band width of the antenna decreases with increase of magnitude of the reactive components. In other words, since the radiation resistance component of the antenna impedance is largely independent of the diameter of the radiator, it will be seen that the eiective band width of the antenna of Figure 1 increases with an increase of diameter of the radiator I0.

Figure 2 illustrates a way in which the reactive variation of the antenna of Figure 1 may be further compensated. Here the quarter wave radiator 20 is of comparatively large transverse dimensions and has a total overall length substantially equal to one half of the operating wavelength. A length of the antenna equal to one quarter of the operating wavelength; that is, substantially half of it, is surrounded by an outer cylinder 2| below the ground plane GP. The upper half of radiator 20 radiates as a large di- .ameter quarter wave radiator perpendicular to ysleeve 2|, are approximately a quarter wave fsleeve 3i). relative to the antennawconductor 2:9 byspacing apart. The enclosed portion of antenna conductor 20 within sleeve 2l thus forms a quarter wave transmission line element which is matched to the antenna resistance while the enclosed transmission line element; that is, the portion of conductor l2 within the hollow lower portion of conductor 20, forms a series reactance in the line. The series reactance in the lineismade as mearly equalto the series rea'ctance of the-'antenna as possible. The two series reactances being substantially a quarter wave apart, one compensates for the other. If necessary, the series reactance in the line may be located at a distance from the antenna feed point as longvfas its fdis'tanceirherefrom is of the order of an lodd number of'ouafrter wavelengths so as to obtain the same compensation effect as before. somewhat upon the particular frequency band requirement since it will be seen thatfa'lar-ge number of quarter waves appear between the two -reactance points inthe system, "a :comparatively small change in frequency may resu-Itxin a .large `total change .in ineffective electrical position. That is, the @chosen-line flengtnmay be an odd number of quarter waves at one frequency `and an even number :at la :slightly different operating frequency if the band width is too great. Such conditions must be avoided. YIt will 'be observed from .the fdrawi-ng that fthe :conductor -20 xhas its lower end spaced `romthe .shea-th l l ".andits -extension which forms the connection -writh the Isleeve 2l., as Well as being spaced Vfrom sleeveZl.

Thus vthe linterior-oit the .hollow 4portionn conductor '20 communicates with the space between conductor 20 and :sleeve i2l for :the `passa/ge -o electromagnetic energy.

In Figure `3 there-is Villustra-ted a means where the radiation resistance of t-he antenna maybe kept more constant. rIfhe antenna and :matching sleeve construction .is the same ain yFigure .3 -as vin Figure 2 and will not again be described. I{Herv-- ever, the `upper -end `of the radiating portion of antenna 20 is here surrounded by a 'conductive Sleeve y3G is 'maintained `lin :position means such as plate r3l fat the-:topfof thefantenna. The 4surrounding 4body karound th'e -top :ci` antenna 2i) effects a redistribution of v`:the eldaabout the antennain such :a way that :oounlter-'effectgis fobtained aga-inst `the eftect'o'f l`the variation .in .fdistribution of the eld by a change infrequently.

"Figure 4 illustrates how .reactance fcorripensation may be applied toa sleeve type off antenna.

.Here the outer sleeve 2l of thetantenna has the upper half above ground plane GP as indi'catedby .51. Thus, the quarter wave :radiator :consists od `two end-'to-end eighth wa-ve xportions, 'energized 'at their junction. '.Due to the change `in position of the ground plane GP withrespect to the :sleewe 2 l the inner member f4!)L is here Ionly ,three .eighfths of a wave in length. YRea'ctan'ce compensation'is applied in this form Eof the inventionby means of a sleeve till lof dielectric 'materialpsunrounding a `selected portion of radiatorrod 40. 11i theldielectric sleeve 4l has a relatively :lrighlliielectric constant, a `suiiicient redistribution for :the :field about vthe :antenna occurs"wheri'aby ia more stant radiation resistanceislobtained. 'The lcon- "ductive radiation redistributing'shieldtw for LFi'gure 3 vmay abe fernployedwith'iligure i4 instead the vdielectric .sleeve '41..

While .I have illustrated .ea t-particnla'r embodiment of the :present invention, itfstrou'ld be fcl'early understood .that vit :is not limited `thereto many :modicatonslmay-be :made the several Such .relocation depends elements employed and in their arrangement without departing from the spirit and scope of the invention.

What is claimed is:

1. An antenna including an elongated conductor having an overall length substantially half of the operating wavelength, substantially one vlialf o *the 'said "conductor being surrounded by "a sleeve, 'at leastI the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and an inner ioonductor, said outer sheath being connected to Isaid sleeve and said inner conductor extending 'into the hollow portion of said conductor, said 'conductor having an opening between the interior of the said hollow portion within said sleeve .and.thelexterior`thereof- 2. rAn antenna including an elongated conductor having an overall length of substantially a half of the operating wavelength, substantially fone hal-f v-o'f l said A:conductor being surrounded by a sleeve, Lat least 2t-he portion of said conductor which is within said :sleeve being hollow., a scoaxial lin'e having I:an outer sheathand 'an inner conductor, `said .outersheath being connected .to said sleeve and said inner conductor extending lintothe hollow portion orsaidconductor :a .distance equalto one quarter :of the voperating"wavelength, Said conductorhaving ran Aopening :pr-oviding communication cr the `passage ci electromagnetic energy between the :interior :of saidlholylow `:portion within asa-id sleeveuand the space between said sleeve-:and said conductor.

.13. .An :antenna .including an elongated .conduc- =tor .having :an overall length of `substantially a half of xthe operating wavelength, substantially Dnc vhalf of `said :conductor lbeing lsurrounded by .a.:sleeve, at Llea'st"-the `port-ion `of .said Vconductor which .is within said .sleeve ibeing hollow, -a coaxial line ihaving an outer :sheath and an inner conductor, said `fouter sheath being connected yto :said ysleeve-and said inner conductor extending intothe `hollow :portion fof said conductor adie- .tance equal to one-quarterof the operating wavelength, a-,portionrofsaid conductor which is outside 4said `sleeve .being surrounded by .means `so re- .d-istributing .the fleldabout .said antenna as to counteractthe variation 'infimpedance of said antenna .with a change 4in ireque'ncy, said conductor having .an opening, .the .interior of .said 'hollow ,portion .of Isaid .conductor communicating throughsaid opening with .the space between the said sleeve and Isaid conductor (for lthe passage .o electromagnetic energy.

4. .An antenna including an elongated conductor, a portion o'f said conductor being 'surrounded by a sleeve having a length equal 'to aquarter o'f the `operating wavelength, at least "the Yportion of said vconductor `vs'vh'ich'is within said sleeve being "hollow, a 'coaxial line having an outer 'sheath an'dan'inner conductor, Vsaid 'outer sheath Abeing connected to"sa'id`sl'eeve andsai'd inner lconductor extending'intothe hollow-portion of said conductor a'dista-nc'eequal to lan odd multiple, including unity,o`f one quarter or `the operatingwavelength, jsaid 'antenna extend-ing V'perpendicular to 'a conductivefs'heeta-'distance equal fto a quarter wavelength, said con'ductor having an opening, vrthe interior 'of saidhollowporti'on "of said conductor #communicating vthrough-said opening with th'e space between the said sleeve and said conductor lcfor the A.passage of electromagnetic energy i5. antenna including 4an 'elongated xconductor `nailing :fan .ioverall V'length ylof .substantially .sa half of the operating wavelength, substantially one half of said conductor being surrounded by a sleeve, at least the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and an inner conductor, said outer sheath being connected to said sleeve and said inner conductor extending into the hollow portion of said conductor a distance equal to one quarter of the operating wavelength, a portion of said conductor which is outside said sleeve being surrounded by means so redistributing the eld about said antenna as to counteract the variation in impedance of said antenna with a change in frequency, said means including a conductive sleeve member surrounding the outer end of outer conductor and connected thereto, said conductor having an opening, the interior of said hollow portion of said conductor communicating through said opening with the space between the said sleeve and said conductor for the passage of electromagnetic energy.

6. An antenna including an elongated conductor having an overall length of substantially a half of the operating wavelength, substantially one half of said conductor being surrounded by a sleeve, at least the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and an inner conductor, said outer sheath being connected to said sleeve and said inner conductor extending into the hollow portion of said conductor a distance equal to one quarter of the operating Wavelength, a portion of said conductor which is outside said sleeve being surrounded by means so redistributing the eld about said antenna as to counteract the variation in impedance of said antenna with a change in frequency, said means including an insulating sleeve of high dielectric material surrounding outer end of said conductor, said conductor having an opening, the interior of said hollow portion of said conductor communicating through said opening with the space between the said sleeve and said conductor for the passage of electromagnetic energy.

7. An antenna including an elongated conductor extending normal to a conductive sheet constituting a ground plane and having an overall length of substantially three eighths of the operating wavelength, a length of said conductor equal to one quarter of the operating wavelength being surrounded by a sleeve, at least the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and inner conductor, said outer sheath being connected to said sleeve and said inner conductor extending into the hollow portion of said conductor a distance equal to one quarter of the operating wavelength, said conductor having an..

opening, the interior of said hollow portion of said conductor communicating through said opening with the space between the said sleeve and said conductor for the passage of electromagnetic energy.

8. An antenna including an elongated conductor extending normal to a conductive sheet conductor equal to one quarter'of the operating Wavelength being surrounded by a sleeve, at least the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and inner conductor, said outer sheath being connected to said sleeve and said.

inner conductor extending into the hollow portion of said conductor a distance equal to an odd multiple, including unity, of one quarter of the operating wavelength, the extension of said antenna above said sheet being one quarter of the operating wavelength, said conductor having an opening, the interior of said hollow portion of said conductor communicating through said opening with the space between the said sleeve and said conductor for the passage of electromagnetic energy.

`9. An antenna including an elongated conductor extending normal to a conductive sheet constituting a ground plane and having an overall length of substantially three eighths of the operating wavelength, a length of said conductor equal to one quarter of the operating wavelength being surrounded by a sleeve, at least the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and an inner conductor, said outer sheath being connected to said sleeve and said inner conductor extending into the hollow portion of said conductor a distance equal to one quarter of the operating wavelength, substantially one half of said sleeve extending above said ground sheet, said tubular conductor having an opening at the end thereof above said sheet.

10. An antenna including an elongated conductor having an overall length of substantially a half of the operating wavelength, substantially one half of the said conductor 4being surrounded by a sleeve, at least the portion of said conductor which is within said sleeve being hollow, a coaxial line having an outer sheath and an inner conductor, said outer sheath being connected to said sleeve and said inner conductor extending into the hollow portion of said conductor, the end of vsaid conductor including said hollow portion within said sleeve being insulatingly spaced from said sheath and said sleeve to aord communication for the passage of electromagnetic energy between the interior of said hollow portion of said conductor and the space between said sheath and said conductor.

NILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,158,271 Buschbeck May 16, 1939 2,239,724 Lindenblad Apr. 29, 1941 2,239,909 Buschbeck et al Apr. 29, 1941 2,297,512 Von Baeyer Sept. 29, 1942 2,323,641 Bailey July 6, 1943 

